graph theory:
    Lets `P = x_0x_1...x_(n-1)` (`n>=3`) is path in graph G = (V, E). Graph `C_n = P + x_(n-1)x_0` is called cycle. Usually denoted `C^n` or `C_n`.
    n is number of edges or vertices in cycle and it is called length of cycle.
    The cycle can be also defined as closed walk, if every pair of vertices except its starting point and ending point are distinct.
    `C_3` = `K_3` (complete graph on 3 vertices or triangle).
    
    Each of the cycles `C_n` and `C_m` (`m, n in NN`) are homeomorphic graphs.
    If `n>=4` then every vertex has a neighborhood isomorphic to `K_2^c`.
    
    group theory:
    other names: m-cycle
    Let `a_1, a_2, ... , a_m` be distinct integers in {1, 2, . . . , n}. If `alpha in S_n` (symmetric group on n-letters) fixes the other integers and if `alpha(a_1) = a_2, alpha(a_2) = a_3, ... , alpha(a_(m−1)) = a_m, alpha(a_m ) = a_1`, then `alpha` is called an cycle.
    
    The name m-cycle is usually used if we need an information about length of cycle.
    
    

    
    Example:
    If we have a cycle `1 -> 3`, `3 -> 4`, `2 -> 2`, `4 -> 1`, we can write:
    `alpha = ((1, 2, 3, 4),(3, 2, 4, 1)) = (1 3 4) (2)`