Izometrie

În matematică o izometrie (sau congruență, sau transformare congruentă) este o transformare în spații metrice care conservă distanța, transformare presupusă de obicei a fi bijectivă.^[2]

^ en Coxeter 1969, p. 46.
3.51 Any direct isometry is either a translation or a rotation. Any opposite isometry is either a reflection or a glide reflection.
^ en Coxeter 1969, p. 29.
"We shall find it convenient to use the word transformation in the special sense of a one-to-one correspondence $P\to P'$ among all points in the plane (or in space), that is, a rule for associating pairs of points, with the understanding that each pair has a first member $P$ and a second member $P'$ and that every point occurs as the first member of just one pair and also as the second member of just one pair...
In particular, an isometry (or "congruent transformation," or "congruence") is a transformation which preserves length..."