Whoops.  Slight coding error there, because I didn't understand what
Croquet.Matrix>>* does.
		"Laplace filter"
		lap := Matrix[3,3] fill: #(1 4 1 4 -20 4 1 4 1).

	lap := Matrix new: 3 tabulate: [:r :c |
		(#((1 4 1) (4 -20 4) (1 4 1)) at: r) at: c]

		image := Matrix[50,50] fill: 1.

	image := Matrix new: 50 element: 1.  "in new version."

		fImage := Matrix[50,50] define:[:i1 :i2|
			(image[(i1-1 to: i1+1), (i2-1 to: i2+1)] * lap) sum sum].

	fImage := Matrix rows: 50 columns: 50 tabulate: [:r :c |
!	    ((image atRows: r-1 to: r+1 columns: c-1 to: c+1) +* lap) sum]

Should read

	fImage := Matrix rows: 50 columns: 50 tabulate: [:r :c |
!	    ((image atRows: r-1 to: r+1 columns: c-1 to: c+1) * lap) sum]


	fImage := Matrix rows: 50 columns: 50 tabulate: [:r :c |
	    ((image atRows: r-1 to: r+1 columns: c-1 to: c+1 ifInvalid: 0)
!	      +* lap) sum]

Should read

	fImage := Matrix rows: 50 columns: 50 tabulate: [:r :c |
	    ((image atRows: r-1 to: r+1 columns: c-1 to: c+1 ifInvalid: 0)
!	      * lap) sum]


	    image := Matrix new: 53: fill: 1.
	    fImage := Matrix new: 50 tabulate: [:r :c |
		(r at c) printString displayAt: 0 at 0.
!		((image atRows: r to: r+2 columns: c to: c+2) * lap) sum]
	
Should read

	    image := Matrix new: 53: fill: 1.
	    fImage := Matrix new: 50 tabulate: [:r :c |
		(r at c) printString displayAt: 0 at 0.
!		((image atRows: r to: r+2 columns: c to: c+2) * lap) sum]
	
!	The examples above have been tested, but where retyped by hand, so may
!	contain typos.
	
Should read
	
!	The examples above have been tested, but where retyped by hand, so may
!	contain typos, and are now known to contain thinkos.