Google Books Ngram Viewer

Graph these comma-separated phrases:
case-insensitive
between and from the corpus with smoothing of .  
Search in Google Books:

1800 - 1980 1981 - 2002 2003 - 2004 2005 - 2006 2007 - 2008 olusegun obasanjo English
1800 - 1972 1973 - 1995 1996 - 1998 1999 - 2002 2003 - 2008 wole soyinka English
1800 - 1963 1964 - 1988 1989 - 1990 1991 - 2003 2004 - 2008 obafemi awolowo English
1800 - 1970 1971 - 1996 1997 - 1998 1999 - 2002 2003 - 2008 chinua achebe English

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