def telescopic_direct(L, R, n, limits):
    """Returns the direct summation of the terms of a telescopic sum

    L is the term with lower index
    R is the term with higher index
    n difference between the indexes of L and R

    For example:

    >>> telescopic_direct(1/k, -1/(k+2), 2, (k, a, b))
    -1/(b + 2) - 1/(b + 1) + 1/(a + 1) + 1/a

    """
    (i, a, b) = limits
    s = 0
    for m in range(n):
        s += L.subs({i: a + m}) + R.subs({i: b - m})
    return s