function checkSolution(solution_string) {

    boxshown = false
    highlight = false
    for (i = 1; i <= solution_string.length; i++) {
	document.getElementById("square" + i).style.background = ""
        if (document.getElementById("square" + i).value != solution_string.substr(i - 1, 1)) {

	    if (boxshown == false) {
		highlight = confirm("The solution is incorrect.  Would you like to highlight all incorrect entries?")
		boxshown = true
	    }

	    if (highlight == true) {
		//		document.getElementById("square" + i).style.border = "3px solid red"
		document.getElementById("square" + i).style.background = "#ff8888"
	    }
        }
    }
    if (boxshown == true) {
	return false
    }
    alert("Solution correct!")
    return true
}