fact: Definition etelescope : (\bar R)^nat := [sequence u_ n.+1 - u_ n]_n.
imports: mathcomp(all_ssreflect ssralg ssrint ssrnum matrix) mathcomp(interval rat) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(set_interval) reals ereal signed topology normedtype landau