GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
12[1XIndex[101X34[2X\in[102X 2.4-25[2XCanEasilyCompareCongruenceSubgroups[102X 2.4-36[5XCongruence[105X package .-17[2XCongruenceSubgroupGamma0[102X 2.1-28[2XCongruenceSubgroupGamma1[102X 2.1-49[2XCongruenceSubgroupGammaUpper0[102X 2.1-310[2XCongruenceSubgroupGammaUpper1[102X 2.1-511[2XDefiningCongruenceSubgroups[102X 2.3-312[2XDenominatorOfGFSElement[102X 3.2-313[2XFareySymbol[102X 4.1-114[2XFareySymbolByData[102X 3.1-115[2XGeneralizedFareySequence[102X 3.2-116[2XGeneratorsByFareySymbol[102X 4.2-417[2XGeneratorsOfGroup[102X 4.2-518[2XIndex[102X 2.4-519[2XIndexInPSL2ZByFareySymbol[102X 4.3-120[2XIndexInSL2Z[102X 2.3-221[2XInfoCongruence[102X 5.1-122[2XIntersection[102X 2.1-623[2XIntersectionOfCongruenceSubgroups[102X 2.1-624[10XIsCongruenceSubgroup[110X 1.1 2.25[2XIsCongruenceSubgroupGamma0[102X 2.2-226[2XIsCongruenceSubgroupGamma1[102X 2.2-427[2XIsCongruenceSubgroupGammaUpper0[102X 2.2-328[2XIsCongruenceSubgroupGammaUpper1[102X 2.2-529[10XIsFareySymbol[110X 3.30[10XIsFareySymbolDefaultRep[110X 3.31[2XIsIntersectionOfCongruenceSubgroups[102X 2.2-632[2XIsPrincipalCongruenceSubgroup[102X 2.2-133[2XIsSubset[102X 2.4-434[2XIsValidFareySymbol[102X 3.1-235[2XLabelsOfFareySymbol[102X 3.2-436[2XLevelOfCongruenceSubgroup[102X 2.3-137[2XMatrixByEvenInterval[102X 4.2-138[2XMatrixByFreePairOfIntervals[102X 4.2-339[2XMatrixByOddInterval[102X 4.2-240[2XNumeratorOfGFSElement[102X 3.2-241[2XPrincipalCongruenceSubgroup[102X 2.1-142[2XRandom[102X 2.4-143one and two argument versions 2.4-1444546-------------------------------------------------------474849