Description: Distribution of class substitution over a left-nested implication. Similar to sbcimg . sbcim2g is sbcim2gVD without virtual deductions and was automatically derived from sbcim2gVD using the tools program translate..without..overwriting.cmd and Metamath's minimize command. (Contributed by Alan Sare, 18-Mar-2012) (Proof modification is discouraged.) (New usage is discouraged.)