sentences. Some sources now state it is acceptable for monospaced fonts to be single spaced today, [ 81 ] although other references continue to specify double spacing for monospaced fonts. [ 82 ] The double space typewriter convention has been taught in schools in typing classes, and that remains the practice in many cases. [ 13 ] Some voice concerns that students will later be forced to relearn how to type. [ 83 ] Most style guides indicate that single sentence spacing is proper for final or published work today, [ 44 ] and most publishers require manuscripts to be submitted as they will appear in publication—single sentence spaced. [ 84 ] Writing sources typically recommend that prospective authors remove extra spaces before submitting manuscripts, [ 85 ] although other sources state that publishers will use software to remove the spaces before final publication. [ 86 ] Claims abound regarding the legibility and readability of the single and double sentence spacing methods—by proponents on both sides. Supporters of single spacing assert that familiarity with the current standard in books, magazines, and the Web enhances readability, that double spacing looks strange in text using proportional fonts, and that the " rivers " and "holes" caused by double spacing impair readability. [ 87 ] Proponents of double sentence spacing state that the extra space between sentences enhances readability by providing clearer breaks between sentences and making text appear more legible, [ 88 ] particularly noting the very small visual difference between a