Determine if a LL(2) grammar is strong
From http://slkpg.com/llkparse.html

Definition:  A grammar G = ( N, T, P, S ) is said to be strong
LL(k) for some fixed natural number k if for all
nonterminals A, and for any two distinct A-productions in the grammar

$A \rightarrow \alpha$

$A \rightarrow \beta$

$FIRST_k ( \alpha \,\, FOLLOW_k (A) ) \cap  FIRST_k ( \beta \,\, FOLLOW_k (A) ) = \emptyset$

That is, each parsing decision is based only on the next k tokens of the
input for the current nonterminal that is being expanded.