As GT.M currently only supports the ANSI X11.1-1995 version of M/MUMPS, it doesn't incorporate extensions made to the standard by Intersystems. As part of code convergence, some version have incorporated Intersystems extensions. These must documented for resolution.
Greater than or equal to expression.
Cache Expression: >=
ANSI Expression: '<
Less than or equal to expression.
Cache Expression: <=
ANSI Expression: '>
The relevant part of the proposed standard is documented at: