pub fn free_type_variables(&self) -> HashSet<usize> {
        type_variables(&self.signature)
            // NOTE `self.difference(other)` == the values that are in self but not in other.
            .difference(&self.forall)
            .copied()
            .collect()
    }
/// Returns the variables mentioned in the signature and not bound in the quantifier.
Returns the variables mentioned in the signature and not bound in the quantifier.
Returns the variables mentioned in the signature and not bound in the quantifier .
pub fn free_type_variables(&self) -> HashSet<usize> {
        type_variables(&self.signature)
            // NOTE `self.difference(other)` == the values that are in self but not in other.
            .difference(&self.forall)
            .copied()
            .collect()
    }
pub fn free_type_variables ( & self ) -> HashSet < usize > { type_variables ( & self . signature ) // NOTE `self.difference(other)` == the values that are in self but not in other. . difference ( & self . forall ) . copied ( ) . collect ( ) }
Returns the variables mentioned in the signature and not bound in the quantifier.
Returns the variables mentioned in the signature and not bound in the quantifier .
&self
&self