diff --git a/Cargo.lock b/Cargo.lock
index f934683b..0e03084b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -81,7 +81,7 @@ dependencies = [
 
 [[package]]
 name = "calcit_runner"
-version = "0.3.0-a7"
+version = "0.3.0-a8"
 dependencies = [
  "cirru_edn",
  "cirru_parser",
diff --git a/Cargo.toml b/Cargo.toml
index 5954101d..2908d1b5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "calcit_runner"
-version = "0.3.0-a7"
+version = "0.3.0-a8"
 authors = ["jiyinyiyong <jiyinyiyong@gmail.com>"]
 edition = "2018"
 license = "MIT"
diff --git a/package.json b/package.json
index f223e225..d10a7740 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@calcit/procs",
-  "version": "0.3.0-a7",
+  "version": "0.3.0-a8",
   "main": "./lib/calcit.procs.js",
   "devDependencies": {
     "@types/node": "^14.14.41",
diff --git a/src/builtins.rs b/src/builtins.rs
index b1f707e9..1aaac9e0 100644
--- a/src/builtins.rs
+++ b/src/builtins.rs
@@ -47,6 +47,7 @@ pub fn is_proc_name(s: &str) -> bool {
       | "&<"
       | "&>"
       | "not"
+      | "identical?"
       // math
       | "&+"
       | "&-"
@@ -166,6 +167,8 @@ pub fn handle_proc(name: &str, args: &CalcitItems) -> Result<Calcit, String> {
     "&<" => logics::binary_less(args),
     "&>" => logics::binary_greater(args),
     "not" => logics::not(args),
+    // in Rust, no real pointer `identical?`, fallback to value equal
+    "identical?" => logics::binary_equal(args),
     // math
     "&+" => math::binary_add(args),
     "&-" => math::binary_minus(args),
diff --git a/src/builtins/sets.rs b/src/builtins/sets.rs
index f838e389..8c44248e 100644
--- a/src/builtins/sets.rs
+++ b/src/builtins/sets.rs
@@ -33,7 +33,15 @@ pub fn call_exclude(xs: &CalcitItems) -> Result<Calcit, String> {
 }
 pub fn call_difference(xs: &CalcitItems) -> Result<Calcit, String> {
   match (xs.get(0), xs.get(1)) {
-    (Some(Calcit::Set(a)), Some(Calcit::Set(b))) => Ok(Calcit::Set(a.clone().difference(b.clone()))),
+    (Some(Calcit::Set(a)), Some(Calcit::Set(b))) => {
+      // im::HashSet::difference has different semantics
+      // https://docs.rs/im/12.2.0/im/struct.HashSet.html#method.difference
+      let mut ys = a.to_owned();
+      for item in b {
+        ys.remove(item);
+      }
+      Ok(Calcit::Set(ys))
+    }
     (Some(a), Some(b)) => Err(format!("&difference expected 2 sets: {} {}", a, b)),
     (a, b) => Err(format!("&difference expected 2 arguments: {:?} {:?}", a, b)),
   }
diff --git a/src/primes.rs b/src/primes.rs
index e8eb1d68..06dd7581 100644
--- a/src/primes.rs
+++ b/src/primes.rs
@@ -408,7 +408,7 @@ impl PartialEq for Calcit {
 pub const CORE_NS: &str = "calcit.core";
 pub const GENERATED_NS: &str = "calcit.gen";
 
-pub const CALCI_VERSION: &str = "0.3.0-a7";
+pub const CALCI_VERSION: &str = "0.3.0-a8";
 
 impl Calcit {
   pub fn turn_string(&self) -> String {