diff --git a/kalk/src/prelude/mod.rs b/kalk/src/prelude/mod.rs
index 00379ee..161599e 100644
--- a/kalk/src/prelude/mod.rs
+++ b/kalk/src/prelude/mod.rs
@@ -107,6 +107,10 @@ lazy_static! {
         m.insert("lcm", (BinaryFuncInfo(lcm, Other), ""));
         m.insert("log", (BinaryFuncInfo(logx, Other), ""));
         m.insert("root", (BinaryFuncInfo(nth_root, Other), ""));
+        m.insert("nCr", (BinaryFuncInfo(ncr, Other), ""));
+        m.insert("comb", (BinaryFuncInfo(ncr, Other), ""));
+        m.insert("nPr", (BinaryFuncInfo(npr, Other), ""));
+        m.insert("perm", (BinaryFuncInfo(npr, Other), ""));
         m
     };
 }
@@ -222,6 +226,7 @@ fn from_angle_unit(context: &mut interpreter::Context, x: KalkNum, angle_unit: &
 pub mod funcs {
     #[cfg(not(feature = "rug"))]
     pub use super::regular::funcs::*;
+    use super::special_funcs::factorial;
     #[cfg(feature = "rug")]
     pub use super::with_rug::funcs::*;
     use crate::kalk_num::KalkNum;
@@ -715,6 +720,16 @@ pub mod funcs {
         KalkNum::new_with_imaginary(x.value.trunc(), &x.unit, x.imaginary_value.trunc())
     }
 
+    pub fn ncr(x: KalkNum, y: KalkNum) -> KalkNum {
+        factorial(x.clone()).div_without_unit(
+            factorial(y.clone()).mul_without_unit(factorial(x.sub_without_unit(y))),
+        )
+    }
+
+    pub fn npr(x: KalkNum, y: KalkNum) -> KalkNum {
+        factorial(x.clone()).div_without_unit(factorial(x.sub_without_unit(y)))
+    }
+
     fn multiply_with_i(z: KalkNum) -> KalkNum {
         // iz = i(a + bi) = -b + ai
         KalkNum::new_with_imaginary(-z.imaginary_value, &z.unit, z.value)
diff --git a/kalk/src/prelude/regular.rs b/kalk/src/prelude/regular.rs
index 5adb16a..0bccdee 100644
--- a/kalk/src/prelude/regular.rs
+++ b/kalk/src/prelude/regular.rs
@@ -50,8 +50,8 @@ pub(crate) mod funcs {
         2f64.sqrt() * pi.sqrt() * t.powf(x - 0.5f64) * (-t).exp() * a
     }
 
-    pub fn bitcmp(x: KalkNum, y: KalkNum) -> KalkNum {
-        KalkNum::from(!x.value.round() as i32)
+    pub fn bitcmp(x: KalkNum) -> KalkNum {
+        KalkNum::from(!(x.value.round() as i32))
     }
 
     pub fn bitand(x: KalkNum, y: KalkNum) -> KalkNum {