Decreasing is a little harder to do. But, again one doesn't have to worry about which way the decrease will lean (as one does in knitting). But, I'm going to talk about cluster sts first.
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*cs (3 tr), ch 2, skip 2*, repeat * to *
with cs standing for cluster stitch and 3 tr showing that 3 triple crochet sts are combined to form the cs. (But, there are very few standard abbreviations in crocheting or, for that matter, very little in the way of standard terminology.)
NexStitch calls a st like this a popcorn, bobble, or puff and reserves the term cluster st to one that creates a decrease.
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Here are some abbreviations.
sc2tog -- single crochet next 2 sts together
tr2tog -- triple crochet next 2 sts together
dc3tog -- double crochet next 3 sts together.
Directions for dc3tog: Start a double crochet st but do not do the last step. Two loops remain on the hook. Start a double crochet st in the next st but do not do the last step. Three loops remain on the hook. Start a double crochet st in the next st but do not do the last step. Four loops remain on the hook . To complete the st, yo and pull the yarn through all loops. The stitch is complete, and just one loop remains on the hook.
After looking at last week's creation, I decided that I wanted it more rounded. So I frogged it to the last lace mesh row and replaced the sc row by:
Turn, ch2, skip 1, *skip 1, dc, ch1* across, ending with skip 1, double crochet together next st with the third st after that. (This takes the st count down to 9 from 15.)
(Then the buttonhole row is:)
ch 1, sc 1, ch 4, skip 5, sc 1, slip st 1.