# river — the wolf/goat/cabbage crossing, taught with the same closed frames
# as hanoi-3 plus two new families: a co-travel effect (the farmer rides every
# crossing) and the "may not be with ... without ..." constraint.
# Lines starting with # are skipped by import.
#
# After `tmct import --file river.txt`, try this in `tmct chat` (or via --prompt):
#
#   wolf-1 stands on bank-east. goat-1 stands on bank-east.
#   cabbage-1 stands on bank-east. farmer-1 stands on bank-east.
#   the goal is that every passenger stands on bank-west. solve it.
#
# The classic optimum is 7 crossings: goat over, farmer back, wolf over, goat
# back, cabbage over, farmer back, goat over. From the opening position exactly
# 1 move is legal (ferry the goat) — every other crossing leaves the wolf with
# the goat, or the goat with the cabbage, without the farmer.
#
# Other things to try:
#   legality  — "what moves are legal now?"  (one ply, no plan; shows the
#               constraint pruning: 1 legal move at the start)
#   read-back — "what stands on bank-east?"  (plain fact question, no planning)
a passenger is a kind of game piece.
a bank is a kind of place.
wolf-1 is a wolf. wolf-1 is a passenger.
goat-1 is a goat. goat-1 is a passenger.
cabbage-1 is a cabbage. cabbage-1 is a passenger.
farmer-1 is a farmer.
bank-east is a bank. bank-west is a bank.
you can ferry a passenger onto a bank.
you can ferry a farmer onto a bank.
ferrying a passenger onto a bank makes the passenger stand on the target.
ferrying a passenger onto a bank makes the farmer stand on the target.
to ferry a passenger onto a bank, the wolf may not be with the goat without the farmer.
to ferry a passenger onto a bank, the goat may not be with the cabbage without the farmer.