0/1 vs true/false

Just having a small argument with an application developer ...

is using 0/1 for boolean types SQL compliant? I am trying to convince
him that the proper SQL compliant (and postgresql compliant) syntax is
true/false but he won't budge ...

The app as currently written no longer works with postgres because they
code uses 0/1 instead of the now enforced true/false for boolean types.

Can someone point me to an SQL spec and section where this is clearly
stated out?

Thanks,

Jean-Christian Imbeault