Update spec.md

spec.md

@@ -338,6 +338,7 @@ def add = a -> b -> a + b
 - `arg -> value`: one-step backwards inferrable lambda
 - `arg: Type -> value`
 - `func(arg1, arg2)`: function application. requires at least one argument. partial function applications are allowed too
+- `func(_, arg)`: bind some args from function, return funciton taking in the args with `_`, or the non-specified ones
 - `expr :: type`: down-cast type
 - `recExpr with fieldname: newFieldValue`: overwrites or adds a field to a record type.
   type checking: identical to `recExpr and {fieldname: newFieldValue}`
@@ -362,7 +363,8 @@ TODO
 ## equality operator
 The only operator with type overloading
 
-TODO
+Compares any two types that can be [phi unified](#phi-unification), returning
+either `'True Unit` `'False Unit` (which maps to `Bool`)
 
 
 # (for users) programming patterns