The LEFT_FUNCTION statement (LFN)
The LEFT_FUNCTION statement has the same syntax as the FUNCTION statement, although the type of the left-hand-function now refers to the type of a received argument rather than a function result.
A FALCON implementation must allow for a regular function and a left-hand function with the same name to coexist within a single program, but this is not required to be true for the original names of external subprograms. (See the description of the ALIAS statement below to find how to give subroutines additional names).