document.write('');
document.write(' 1950s |');
document.write(' 1960s |');
document.write(' 1960s P2 |');
document.write(' 1960s P3 |');
document.write(' 1960s P4 |');
document.write(' 1960s P5 |');
document.write(' 1960s P6 |');
document.write(' 1970s |');
document.write(' 1970s P2 |');
document.write(' 1970s P3 |');
document.write(' 1980s');
document.write('');