FIRST_TCL : (thm_tactical list -> thm_tactical)
STRUCTURE
Thm_cont
SYNOPSIS
Applies the first theorem-tactical in a list which succeeds.
DESCRIPTION
When applied to a list of theorem-tacticals, a theorem-tactic and a theorem, FIRST_TCL returns the tactic resulting from the application of the first theorem-tactical to the theorem-tactic and theorem which succeeds. The effect is the same as: 
   FIRST_TCL [ttl1;...;ttln] = ttl1 ORELSE_TCL ... ORELSE_TCL ttln

FAILURE
FIRST_TCL fails iff each tactic in the list fails when applied to the theorem-tactic and theorem. This is trivially the case if the list is empty.
SEEALSO
EVERY_TCL, ORELSE_TCL, REPEAT_TCL, THEN_TCL
HOL  Kananaskis-14