feat(frontends/lean): nicer notation for dependent if-then-else
feat(library/definitional): add "datastructure" for storing recursive equations
feat(library/definitional/equations): add support for serializing equations
feat(frontends/lean): parse "decreasing" expressions
chore(library/definitional/equations): fix style
refactor(frontends/lean/decl_cmds): cleanup definition_cmd
feat(frontends/lean): parse recursive equations
feat(hott/types/sigma): complete prove, finish porting sigma, clean-up names
style(hott/axioms/funext): rename path_forall and make arguments implicit
squash into previous, make instance in funext work; also some minor style fixes in other files
completely finish sigma, squash
squash, more in pi