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    Date: Mon 2 Jan 89 17:31:11-PST
    From: Kim A. Barrett <IIM@ECLA.USC.EDU>


     Extend SUBTYPEP to accept an optional third argument.  This argument should be
     either NIL, the &environment argument received by a macro expander function,
     or the environment argument received by an *evalhook* or *applyhook* function.
     This argument is used to distinguish between compile-time and run-time

I can't imagine why you would add an environment argument to SUBTYPEP,
but not to TYPEP.  In any case, the CLOS plan for this was that anyone who
needed to use a non-null environment would call FIND-CLASS explicitly,
instead of relying on the implicit class inside TYPEP and SUBTYPEP.
Since use of the compile-time environment for types should be quite rare,
this was seen as much less of a burden than modifying existing functions
to take new optional arguments.