This tutorial shows you how to knit the SSP (slip, slip, purl) single decrease, which reduces the number of the stitches on the needles by one, and is pretty much always done on a purl row.
The SSP is the purl equivalent of the SSK decrease, is left leaning, and if it is to be paired with another decrease, it will no doubt be paired with the right leaning P2tog decrease.
I then show you how to do the SSSP (slip, slip, slip, purl) decrease which is a double decrease i.e. it reduces the number of stitches on the needles by two, and is also left leaning. It would be paired up with the right leaning P3tog decrease.
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