Liquid: Circuit Feature Negotiation
MMP defines a circuit feature negotiation strategy which is currently being overhauled (= überarbeitet). Implementations exist in perlpsyc and FORK (an inactive part of code in psyced).
Solid: Protocol Switch
This a technique used between psyced's to detect when they are talking XMPP to each other and quickly upgrade to their native protocol. See the details on Protocol Switch.
See also the idea on "How to enhance IRC with PSYC Authentication".