diff --git a/.github/workflows/mdbook-check.yml b/.github/workflows/mdbook-check.yml
index 1f991e4..4d693b2 100644
--- a/.github/workflows/mdbook-check.yml
+++ b/.github/workflows/mdbook-check.yml
@@ -21,6 +21,7 @@ jobs:
         run: |
           curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf -y | sh
           rustup update
+          rustup toolchain install nightly-x86_64-unknown-linux-gnu
           cargo install --version ${MDBOOK_VERSION} mdbook
           cargo install --version ${MDBOOKKATEX_VERSION} mdbook-katex
       - name: Build with mdBook
diff --git a/src/backends/plonky2/mock_main/mod.rs b/src/backends/plonky2/mock_main/mod.rs
index f5352e5..a033f7b 100644
--- a/src/backends/plonky2/mock_main/mod.rs
+++ b/src/backends/plonky2/mock_main/mod.rs
@@ -507,7 +507,7 @@ pub mod tests {
             zu_kyc_pod_builder(&params, &gov_id_pod, &pay_stub_pod, &sanction_list_pod)?;
 
         let mut prover = MockProver {};
-        let kyc_pod = kyc_builder.prove(&mut prover)?;
+        let kyc_pod = kyc_builder.prove(&mut prover, &params)?;
         let pod = kyc_pod.pod.into_any().downcast::<MockMainPod>().unwrap();
 
         println!("{:#}", pod);
@@ -520,10 +520,11 @@ pub mod tests {
 
     #[test]
     fn test_mock_main_great_boy() -> Result<()> {
+        let params = middleware::Params::default();
         let great_boy_builder = great_boy_pod_full_flow()?;
 
         let mut prover = MockProver {};
-        let great_boy_pod = great_boy_builder.prove(&mut prover)?;
+        let great_boy_pod = great_boy_builder.prove(&mut prover, &params)?;
         let pod = great_boy_pod
             .pod
             .into_any()
@@ -539,9 +540,10 @@ pub mod tests {
 
     #[test]
     fn test_mock_main_tickets() -> Result<()> {
+        let params = middleware::Params::default();
         let tickets_builder = tickets_pod_full_flow()?;
         let mut prover = MockProver {};
-        let proof_pod = tickets_builder.prove(&mut prover)?;
+        let proof_pod = tickets_builder.prove(&mut prover, &params)?;
         let pod = proof_pod.pod.into_any().downcast::<MockMainPod>().unwrap();
 
         println!("{}", pod);
diff --git a/src/frontend/mod.rs b/src/frontend/mod.rs
index fe53261..7525752 100644
--- a/src/frontend/mod.rs
+++ b/src/frontend/mod.rs
@@ -1,7 +1,7 @@
 //! The frontend includes the user-level abstractions and user-friendly types to define and work
 //! with Pods.
 
-use anyhow::Result;
+use anyhow::{anyhow, Error, Result};
 use itertools::Itertools;
 use std::collections::HashMap;
 use std::convert::From;
@@ -348,7 +348,7 @@ impl MainPodBuilder {
         self.public_statements.push(st.clone());
     }
 
-    pub fn prove<P: PodProver>(&self, prover: &mut P) -> Result<MainPod> {
+    pub fn prove<P: PodProver>(&self, prover: &mut P, params: &Params) -> Result<MainPod> {
         let compiler = MainPodCompiler::new(&self.params);
         let inputs = MainPodCompilerInputs {
             // signed_pods: &self.input_signed_pods,
@@ -357,7 +357,7 @@ impl MainPodBuilder {
             operations: &self.operations,
             public_statements: &self.public_statements,
         };
-        let (statements, operations, public_statements) = compiler.compile(inputs)?;
+        let (statements, operations, public_statements) = compiler.compile(inputs, params)?;
 
         let inputs = MainPodInputs {
             signed_pods: &self.input_signed_pods.iter().map(|p| &p.pod).collect_vec(),
@@ -462,15 +462,27 @@ impl MainPodCompiler {
         middleware::Operation::op(mop_code, &mop_args).unwrap()
     }
 
-    fn compile_st_op(&mut self, st: &Statement, op: &Operation) {
+    fn compile_st_op(&mut self, st: &Statement, op: &Operation, params: &Params) -> Result<()> {
         let middle_st = self.compile_st(st);
         let middle_op = self.compile_op(op);
-        self.push_st_op(middle_st, middle_op);
+        let is_correct = middle_op.check(params, &middle_st)?;
+        if !is_correct {
+            // todo: improve error handling
+            Err(anyhow!(
+                "Compile failed due to invalid deduction:\n {} ⇏ {}",
+                middle_op,
+                middle_st
+            ))
+        } else {
+            self.push_st_op(middle_st, middle_op);
+            Ok(())
+        }
     }
 
     pub fn compile<'a>(
         mut self,
         inputs: MainPodCompilerInputs<'a>,
+        params: &Params,
     ) -> Result<(
         Vec<middleware::Statement>, // input statements
         Vec<middleware::Operation>,
@@ -484,7 +496,7 @@ impl MainPodCompiler {
             public_statements,
         } = inputs;
         for (st, op) in statements.iter().zip_eq(operations.iter()) {
-            self.compile_st_op(st, op);
+            self.compile_st_op(st, op, params)?;
             if self.statements.len() > self.params.max_statements {
                 panic!("too many statements");
             }
@@ -570,7 +582,7 @@ pub mod tests {
         println!("{}", kyc);
 
         let mut prover = MockProver {};
-        let kyc = kyc.prove(&mut prover)?;
+        let kyc = kyc.prove(&mut prover, &params)?;
 
         // TODO: prove kyc with MockProver and print it
         println!("{}", kyc);
@@ -595,4 +607,30 @@ pub mod tests {
 
         Ok(())
     }
+
+    #[test]
+    #[should_panic]
+    fn test_false_st() {
+        let params = Params::default();
+        let mut builder = SignedPodBuilder::new(&params);
+
+        builder.insert("num", 2);
+
+        let mut signer = MockSigner {
+            pk: "signer".into(),
+        };
+        let pod = builder.sign(&mut signer).unwrap();
+
+        println!("{}", pod);
+
+        let mut builder = MainPodBuilder::new(&params);
+        builder.add_signed_pod(&pod);
+        builder.pub_op(op!(gt, (&pod, "num"), 5));
+
+        let mut prover = MockProver {};
+        let false_pod = builder.prove(&mut prover, &params).unwrap();
+
+        println!("{}", builder);
+        println!("{}", false_pod);
+    }
 }
diff --git a/src/middleware/operation.rs b/src/middleware/operation.rs
index 3b921b1..fac4437 100644
--- a/src/middleware/operation.rs
+++ b/src/middleware/operation.rs
@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use std::fmt;
 
 use anyhow::{anyhow, Result};
 
@@ -265,3 +266,14 @@ impl Operation {
         }
     }
 }
+
+impl fmt::Display for Operation {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        writeln!(f, "middleware::Operation:")?;
+        writeln!(f, "  {:?} ", self.code())?;
+        for (i, arg) in self.args().iter().enumerate() {
+            writeln!(f, "    {}", arg)?;
+        }
+        Ok(())
+    }
+}