A RENAME statement is ignored if the L-name is not encountered
in the input.
A RENAME statement for an L-name is valid provided all of the following are true:
The L-name was not already mapped because of a rule that preceded
the RENAME statement rule in the hierarchy described in Mapping L-Names to S-Names.
The L-name was not already mapped because of a previous valid
RENAME statement for the L-name.
The S-name is not itself an L-name. This rule holds true even
if the S-name has its own RENAME statement.
A previous valid RENAME statement did not rename another L-name
to the same S-name.
Either the L-name or the S-name is not defined. Either the L-name
or the S-name can be defined, but not both. This rule holds true even
if the S-name has its own RENAME statement.