function show(id, nohide) {
	divs = ['introduction', 'approach', 'approach2', 'principals', 'principals2', 'contact'];
	
	// get index of anything already being shown
	shown = -1;
	for (i = 0; i < divs.length; i++) {
		if (document.getElementById(divs[i]).style.display == 'block') {
			shown = i;
			break;
		}
	}

	if (shown > -1) {
		// something shown, see if the current div has been selected again
		if (id == divs[shown] || (id == 'principals' && divs[shown] == 'principals2' && !nohide) || (id == 'approach' && divs[shown] == 'approach2' && !nohide)) {
			// yes, hide it
			document.getElementById(divs[shown]).style.display = 'none';
		} else {
			// no, just swap shown divs
			document.getElementById(divs[shown]).style.display = 'none';
			document.getElementById(id).style.display = 'block';
		}
	} else {
		// nothing shown, show selected div
			document.getElementById(id).style.display = 'block';
	}
}