C++ binary predicate implementation requirements

On this site it states that for a binary predicate:

The types Type1 and Type2 must be such that objects of types ForwardIt1 and ForwardIt2 can be dereferenced and then implicitly converted to both Type1 and Type2.

However, in the C++ International Standard documentation I see no reference to such a constraint. I am wondering if this constraint is explicitly stated in the C++ International Standard documentation which section it is under. In addition if it is not then why is this constraint placed upon the std::search function as isn't it possible to have two distinct types that while not implicitly convertible have an equality operator overload defined?