[ BeginEnv "proposition"
, Label "in_irrefl"
, Word "for"
, Word "all"
, Word "sets"
, BeginEnv "math"
, Variable "A"
, EndEnv "math"
, Word "we"
, Word "have"
, BeginEnv "math"
, Variable "A"
, Command "not"
, Command "in"
, Variable "A"
, EndEnv "math"
, Symbol "."
, EndEnv "proposition"
, BeginEnv "proof"
, BracketL
, Word "proof"
, Word "by"
, Command "in"
, Word "-induction"
, BracketR
, Word "straightforward"
, Symbol "."
, EndEnv "proof"
]