For hip slant co 4 x 1 st in every 4th row (3 x 1 st in every 4th row, then 1 x 1 st in foll 6th row) on both sides = 46 (52) sts.
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Sound to me like “cast off 4 times: 1 sts in every 4th row (3 times: 1 st in each 4th row, and once in the following 6th row) on both sides.”
The cast on was 54 (60) and result will be 46 (52) sts. Since the sentence end with “on both sides” 4 repeats of 2 sts cast off = -8 and 3 reps of 2 dec plus 1 rep of 2 dec = -8 so both sizes result in 46 (52) sts.
or
row 4, 8, 12: cast off 1 both edges.
row 16 (18) cast off 1 both edges.
or
Literal translation: For hip slant cast off 4 times, 1 st in every 4th row (or 4 times, 1 st in row 4,8,12,18) on both sides resulting in 46 (52) sts.
Yeah, that is an odd way to code it.
There, Sue, have I used enough words? 
Oh and the Abbreviation list includes a dec but not a co. The dec is not used in the pattern (nor is dc for UK double crochet or US sc unless I miss my guess). So I think they do me cast off and not decrease when they use co. but I have been wrong before :eyebrow2:
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