The book separates sex-linked biological infrastructure from acquired influences such as language, culture, fantasy, social roles and online experience, all of which can physically remodel the mind. It introduces quantitative tools for comparing local mental states, whole-system architectures and transitions between attractors. It also examines four routes of social inference, autism-related differences in self-modelling, and transgender identification. The central conclusion is cautious: cross-sex-like states may occur, but they do not by themselves demonstrate complete opposite-sex mental equivalence.