#! /usr/bin/gawk -f

# Input is a list of words "w[1]", .. "w[n]", one per line.
# Output is a list of all pairs of consecutive words,
#   "w[i-1] w[i]" for all i in [1..n], one per line.  
# The two words in each pair are separated by a space.
# The word "w[0]" on the first pair is "=" by convention.

BEGIN { want = "=" }

/./ { 
  print (want " " $0)
  want = $0
  next
}