Good Joke. INC is a userdefined function used in all PL/I manuals by IBM.
Assuming that the INC function increments the value of the argument passed to it and returns the updated value, the example that follows could
put out B(1,2) or B(2,1) depending on which subscript is evaluated first. You should not presume which subscript is evaluated first.
I = 0;
put list ( B( INC(I), INC(I) ) );