cross-correlation (sequence1 sequence2 max-lag &optional (min-lag 0))
Returns a list of the correlation coefficients for all lags from
min-lag' to max-lag,' inclusive, where the `i'th list element is the
correlation of the first (length-of-sequence1 - i) elements of
sequence1 with with the last i elements of sequence2. Both sequences
should be sequences of numbers and of equal length.