refactor(library/init): move num->nat coercion to init
test(tests/lean/slow): add "manual" 'path induction' tactic
feat(frontends/lean/pp): add hard-coded pretty printer for nat numerals
feat(library/definitional/brec_on): simplify universe level constraints for non-reflexive recursive datatypes
fix(tests/lean): to reflect recent changes
chore(frontends/lean/pp): fix style
fix(library/tactic/inversion_tactic): bug in mutually recursive case
fix(library/tactic/inversion_tactic): add missing case
refactor(library/unifier): remove dead code
fix(library/unifier): postpone class-instance constraints whose type could not be inferred
feat(frontends/lean): add 'print notation' command
fix(init/reserved_notation): remove "invisible" character at `\/`
fix(library/flycheck): crash when io_state_stream is destroyed before flycheck_scope
refactor(library/algebra/order): change strong order pair, adopt new naming conventions
refactor(library/algebra): use new naming conventions, add information to speed up proofs
fix(library/unifier): assertion violation