Inconsistency on A. Graves' original Connectionist Temporal Classification (CTC) paper?
The lecture I take from the paper is not that equation (6) is a recursive form of (5). In (5), the equation refers to label sequence $l$, while (6) refers to $l^\prime$, which is a modified version of $l$ with blanks added to the
beginning and the end and inserted between every pair of labels. See the paragraph between equations (5) and (6):


  To allow for blanks in the output paths, we consider a modified label sequence l, with blanks added to the beginning and the end and inserted between every pair
  of labels. The length of l is therefore 2|l| + 1. In calculating the probabilities of prefixes of l we allow all transitions between blank and non-blank labels, and also those between any pair of distinct non-blank labels.