TL;DR:
The operations are well defined according to the draft C++ standard.
Details
We can see that by going to the draft C++ standard section 5.9 Relational operators which says (emphasis mine going forward):
The operands shall have arithmetic, enumeration, or pointer type, or type std::nullptr_t. The operators
< (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) all yield
false or true. The type of the result is bool
and bools are arithematic types from 3.9.1 Fundamental types
Types bool, char, char16_t, char32_t, wchar_t, and the signed and unsigned integer types are collectively
called integral types.
and
Integral and floating types are collectively called arithmetic
types.
and true and false are boolean literals from 2.14.6 Boolean literals:
boolean-literal:
false
true
Going back to section 5.9 to see the mechanics of the relational operators further, it says:
The usual arithmetic conversions are performed on operands of arithmetic or enumeration type.
the usual arithmetic conversions are covered in section 5 which says:
Otherwise, the integral promotions (4.5) shall be performed on both operands
and section 4.5 says:
A prvalue of type bool can be converted to a prvalue of type int, with false becoming zero and true
becoming one.
and so the expressions:
false < false
false < true
true < false
true < true
using these rules become:
0 < 0
0 < 1
1 < 0
1 < 1