Factorial[3] -> 3*Factorial[2] -> 3*2*Factorial[1] -> 3*2*1 -> 6*1 -> 6
x2 + 3y2 = Plus[Power[x, 2], Times[3, Power[y, 2]]]
{1, 2, 3} = List[1, 2, 3] First[List[a_, __]] := a First[{1, 2, 3}] -> 1
{# + 1}& /@ {1, 2, c, 4} = Map[{# + 1}&, {1, 2, c, 4}] -> {2, 3, c, 5}
trainingset = {1 -> "A", 2 -> "A", 3.5 -> "B", 4 -> "B"} c = Classify[trainingset] c[2.6] c[2.6, "Probabilities"]
By Alexander Letov
Brief presentation of Wolfram Language