Switching to latest lambdapi syntax

.github/workflows/type_check.yml

encodings/bool_plus.lp

encodings/builtins.lp

encodings/deptype.lp

encodings/equality.lp

encodings/equality_tup.lp

encodings/if.lp

encodings/lhol.lp

encodings/logical.lp

encodings/prenex.lp

encodings/pvs_cert.lp

encodings/pvs_cert_minus.lp

encodings/pvs_core.lp

encodings/sum.lp

encodings/tuple.lp

encodings/unif_rules.lp

paper/proof_irr.lp

paper/stack.lp