Classic distinct-subsequences 2D DP:
dp[i][j] = dp[i-1][j] + (s[i-1] = t[j-1] ? dp[i-1][j-1] : 0)
dp[i][0] = 1 (empty t is a subseq of any prefix of s)
count_subseq "rabbbit" "rabbit" = 3
The three witnesses correspond to which 'b' in "rabbbit" is
dropped (positions 2, 3, or 4 zero-indexed of the run of bs).
Complements subseq_check.ml (just tests presence); this one counts
distinct embeddings.
Tests 2D DP with Array.init n (fun _ -> Array.make m 0), base row
initialization, mixed string + array indexing.
175 baseline programs total.
giles
6780acd0af